Downvoted because it relies on what i like to call the "Required Ratman Den" bad design staple. Portal 2 is a puzzle game based on knowing what you have to work with. It's even in your description for God's sake. The moment you deviate from that structure and require the player to notice something they can't reasonably be expected to notice, you know you have failed as a level designer.

Didn't see the companion cube and brought the regular cube back ito the main part which made it impossible to put the regualr cube back onto the square button. I then had to read the map and restart Apart from that it was alright.